Method and apparatus for treating separating suspensions



Sept. 25, 1951 P. s. BAKELS 2,569,141

METHOD AND APPARATUS FOR TREATING SEPARATING SUSPENSIONS Filed Dec. 10, 1946 Inventor P IETER S. BAKELS AHorneys Patented Sept. 25, I 1951 2569,141 erraranis.rosmm SEPAltAT-ING SUSPENSIONS Pieter s; Bakels; Geleen, Nether ands, assignor to De Directie van de Staat'srnijhe'n in Liinhiirg,

acting *for and on behalf of the State of the Netherlands, Heerlen, Netherlands Application member 10, 1946, Serial Nefna'zzv 4 Claims .1 in w'ashery plants using separating suspensions, it is necessary, for practical operation, to recover and reuse the suspension particles re"- sulting from the de watering. and rinsing of the separated products. For one thing, the sos em sion particles are generally of too-great value to be tl'irown away and,=additionally,' the contamination of the separated products bythe 'sus pension particles is unpermissible. In the case of coal, for example. these suspension articles would increase the ash content of the cleaned coal. V

The suspension caught beneath the screens is very dilute. It has been customary heretofore to send this dilute suspension to a second screen with very nice meshes. This second screen must have ahighcapacityanddue tc -its-fine meshes, it wears out quickly.

In the separation of raw coal in a Washing bo ii using a separating suspension, the suspension particles become contaminated with small coal articles already present upon delivery of the raw coal to the washing box and resulting also from disintegration arising from the. action in the box. It is usually desirable to recover these coal particles since they are of value in themselves and, moreover, should be removdgfrom the separating suspension since they adversely at feet the latter.-

A principal object of the present invention is to greatly reduce the scope of the second screen'- m2- action By separating the suspension into frat heirs of relatively high concentration and relatively low concentration, substantially all of the suspension particles of the low concentration fraetionbeing smaller-than a redetermined sizei Hence, by the invention it is only necessary to screen the fit't'ct-ioh of relatively high concentra-- tion ior the reinoval of unwanted particles above the saidpredeterniined size. It is also an object of the invention to recover the coal particles from the suspension. Suitable apparatus for the practice or the invention is shown by way of ex ample in th''ac'cor'n'pahyirig drawing in which:

Figure 1 diagrammatically shows an'iiistalla tio'n and Figure 2 shows in axial section a cyclone which appears in Figure l;

Referring. to Figure 1, reference numeral 5 designates a washing box or the sink -fioat' type or known design, the hon discharging atone end onto a screen 6. and at its'other end onto a screen 1, receiving tanks 8 and 9 being disposed below the screens. waterasc particles which will pass the screen drop therethrough immediately upon delivery to the sffis ans s ray heads I and I I are provided above the screens so as to the separated products as thoroughly as pessitie as they pass along the screens.

V The tanks have bottom outlets connected through pipes l2 and I3 to a pipe l4 which a' livers to a separator l5 here shown as biiigl of the froth flotation type and acting also as a hydraulic classifier. Preferably a Klinbentiiiek machine is used, theinachine including a gem erally conical tank IS with froth remevai at H, a surhp lB and a riser l9 to a "side overflow trough 2B. A machine of this type dc's'c'iibdoh PagS IBO to 432 Of fThe Cleaning 0f C 0a1fl1928) by Chapman and Mott. Because the Kleinheiw tinclc machine is to operate as a hydrtm li'c classi her as well as a froth flotation unit, it will-1h d the following arrangement. inner Ihbi' IBGof truncated cone shape is centrally disposed in the tank l6 and contains a screw I6 er; a shaft 182 driven by a pulley I63. The diluted suspension froin line I4 is admitted to the-inner mixing chamber Hill through a pipe {411 and a frothirrg agent is'atld'ed at the top of thischaiii her. The materials are thoroughly iniit'ecl in chaifhber I66 and pass with entrained air through the holes lli ldisposed close to the base I or the mixing chamber into the Olitr chm'ibl 6i Slli'fii l8. 7 At about half the height of the iitei' 'chaiii= ber'an annular screen N56 is fiiied horisntally to insure quiescent conditions in the space above it. The frothed coal particles pass througlith'e screen andare scraped off by a scraper I61 ihto a surrounding launder H. The non floatihg ma= terial returns through a series of holes I69 tothe mixing ohaniber, where it is again agitated;

Finally, the particles pass through the openings [l0 into the lower cone Ill and are discharged through a pipe l5. This fraction contains these particles which have the highest settling velocity. viz., the coarser particles. The finer particles which settle slower are evacu'atd through the pipe l9 and an overflow 20 together with the t'iiillt of the Water. The purpose of this ovifiow jih it Kleinbentinck machine is to maintain the level of the liquid in the frothing chamber constant. If this level is too high, too much water and fine heavy particles discharge with the froth. sump hasa bottom opening 15' discharging onto a screen 2| above a receptacle 2-2 and a, pipe 23 leads from a bottom opening l5 of the receptacle to a pump 24, trough Zfl having a bottom outlet connected'by a pipe 25 with pipe 23; The pump delivers through a pipe 26 tangentially into the inlet compartment 21 of a cyclone 28, the cyclone including an upper cylindrical portion 29 divided by a wall 30 into the mist criripQrth'inli'QhQ overflow compartment 3!, the wall having a central outflow opening 32. The cyclone comprises a lower conical portion 33 coaxial with portion 29 and having an apex opening 34 aligned with opening 32. The apex discharge, Figure 1, is directed to the washing box 5 through a conduit 35. The overflow chamber is connected by a pipe 36 with pipe 31 and 38 going to the spray heads l and I I respectively.

In the operation of the system, the dilute suspension reaching the separator I is separated into three fractions; (1) a froth fraction leaving at I! and containing the undesirable coal particles which can be sent, for. example, to a froth flotation plant to be recleaned, as the ash content of this froth may be rather high; (2) an overflow fraction to trough 20 containing fine suspension particles which can be used again in the separatin bath; and (3) a thickened fraction leaving thesump through bottom opening l5 and containing undesired coarser particles in addition to the usable suspension particles. Fraction #3 goes to the screen 2| and the through-put of the screen is combined with fraction #2 and sent to the cyclone thickener with the thickened product being then returned to the washing box. While va cyclone thickener is preferred, other types, for example, the Dorr type, can be used.

- An example of performance is as follows: The

output products of a washing box, using a loess suspension, are de-Watered and rinsed on the screens 6 and l at the rate of 80 metric tons per hour. The diluted suspension caught in tanks 8 and 9 at the rate of 65 cubic meters per hour has a, concentration of 94.4 grams per liter, and 5% of the particles are above .5 mm. in size. This suspension is sent to a Kleinbentinck machine as described above with a diameter of 2 meters and the entering suspension will be separated in this box into (1) 1.8 cubic meters per hour froth, (2) 44.3 cubic meters per hour efiiuent with a concentration of 80 grams per liter solid material of which the particles are all less than .5 mm. in size, and (3) 18.9 cubic meters per hour of thickened suspension with a concentration of 121.5 grams per liter solid material of which 13.3% has a particle size greater than .5 mm.

Fraction number 3 goes to the screen 21 of which the openings are .5 mm. square. The area of the screen is one square meter.

Thus, the capacity of screen 2| need be only suflicient to accommodate a relatively small percentage of the total dilute suspension collecting in tanks 8 and 9. If the diluted suspension went directly to the screen, the latter would have to have an area of 3 square meters. Without removal of the fine coal particles they would recirculate and accumulate. However, if it is not required that the coal particles in the dilute suspension be recovered, any suitable separator, for example a cyclone, which will separate the bulk ofthe particles from the bulk of the water can be used.

- The described procedure is of especial importance if the content of fine solid material in the dilute suspension is high.

Variations in procedure and form of apparatus arepossible within the scope of the invention as defined in the following claims.

. I claim:

1. In combination, a washing box using a separating suspension, screens arranged to receive the separated fractions, rinsing spray heads above the screens, tanks below the screens to receive sprayed liquid and suspension, a hydraulic classifier in receiving relation to said tanks and operating to separate the received suspension into fractions of relatively high concentration and relatively low concentration of which the former contains all theparticles larger. than a predetermined size and aportionof particles smaller than said size, a screen arranged to receive the fraction of high concentration and having a mesh of said predetermined size, a receptacle arranged to receive the through-put of the last-named screen, a thickener, means for feeding to the thickener the suspension received in said receptacle to-- gether with said fraction of low concentration, and means for directing the heavy fraction from the thickener to said washing box.

2. In combination, a coal washing box using a separating suspension, screens arranged to receive the separated fractions, tanks below the screens to receive sprayed liquid and suspension, rinsing spray heads above the screens, a classifier in receiving relation'to said tanks and including means to separate coal particles from the suspension particles by froth flotation and means tohydraulically separate the remaining suspension into fractions of relatively high concentration and relatively low concentration of which the former contains all the particles larger than a predetermined size and a portion of the particles smaller than said size, a screen arranged to receive the fraction of high concentration classifier and having a mesh of said predetermined size, a receptaclearranged to receive the through-put of the last-named screen, a thickener, means for feeding to the thickener the suspension received in said receptacle together with said fraction of low concentration, and means for directing the heavy fraction from the thickener to said washing'box.

3. The-method of treating a separating suspension of liquid and particles which comprises rinsing the suspension from the separated products, separating the thus obtained diluted suspension by hydraulic classification into a'fraction of relatively high concentration and a fraction of relatively low concentration and so that the fraction f high concentration contains all the particles larger than a predetermined size and a portion of the particles smaller than said: size, screening the last-mentioned fraction to remove particles above said size, combining'the throughput of said screening with the fraction'of low concentration, and thickening said combined fractions and returning them to the washing box.

4. The method of treating a wash box separating suspension containing intermixed coal particles which comprises rinsing the suspension from the separated products, separating the coal particles from the thus obtained diluted suspension by froth flotation and separating the remainder of the diluted suspension by hydraulic classification into a fraction of relatively high concentration and a fraction of relatively low concentration and so that the fraction of high concentration contains all the particles larger PIETER s. BAKELSQ (References on following page) REFERENCES CITED UNTTED STATES PATENTS 2,429,436 Walker -11..- Oct. 21-, 1947 FOREIGN PATENTS Number Country fiate 215,615 Great Britain May 15,- 1924 496,538 Great Britain Dec. 2, 1938 OTHER REFERENCES Heavy Media Separation Process, American Cyanamid ore- Dressing Notes July 1942, The Central Mill, pages 14, 15, 16 and 1'7.- 

